The invention relates to a method for the preparation of fine hexagonal ferrite powders, destined in particular for magnetic recording.
Hexagonal ferrites (hexaferrites) are ferrimagnetic materials having a general chemical formula: EQU AReO.BMeO.CFe.sub.2 O.sub.3
where:
A, B and C are stoichiometric indices which vary with the different hexaferrite phases (denoted generally by capital letters M, Y, W, Z and c.); PA1 Re is usually an alkaline earth metal such as barium or strontium; and PA1 Me is a divalent transition metal which, apart from iron, might be zinc, cobalt, copper, manganese, magnesium or nickel.
The magnetic properties of this particular class of materials render them suitable, either in their normal state or appropriately doctored, for a great number of applications; one such application of significant interest is that of magnetic recording.
Reference is made throughout the description to a hexaferrite in the M phase, where A=1, B=0 and C=6, thus producing a chemical formula EQU ReO.6Fe.sub.2 O.sub.3
It will be observed, nonetheless, that the method as disclosed can be applied with hexagonal ferrites in different phases, that is, having different stoichiometric indices.
The object of the method disclosed is to permit of obtaining hexaferrites the physical and the magnetic properties of which -viz, the dimensions of the powdered particles, uniformity of the compound, anisotropy, coercivity, magnetization and c., can be controlled with ease, thereby making it possible to engineer values for the single properties as near as possible to the optimum values effectively required, these being dependent on the ultimate application of the single hexaferrite product.
An advantage of the method is that it permits of obtaining a hexaferrite precursor featuring uniformity of atomic structure and enabling formation of the end product (the hexaferrite) at low temperature applied for a relatively short duration, in such a way as to extract finer particles and generally enhance the granulometry of the powder.